1. Field of the Invention
The present invention relates to a zoom lens which is suitable for use in a broadcasting television camera, a video camera, a digital still camera, and a silver halide film camera, and to an image pickup apparatus including the zoom lens.
2. Description of the Related Art
In recent years, there has been demanded a zoom lens having a high aperture ratio, a high zoom ratio, and high optical performance for an image pickup apparatus such as a television camera, a silver halide film camera, a digital camera, and a video camera.
Positive lead telephoto type four-unit zoom lenses, in which four lens units are provided in total, and one of the lens units located closest to an object side has positive refractive power, have been known as zoom lenses having a high zoom ratio.
This four-unit zoom lens includes, in an order of from the object side to the image side, a first lens unit having positive refractive power for focusing, a second lens unit having negative refractive power for varying magnification, a third lens unit for correcting image plane variation due to magnification-varying, and a fourth lens unit having positive refractive power for imaging.
As to this four-unit zoom lens, there is known a four-unit zoom lens utilizing a so-called three-unit inner focus type (see Japanese Patent Application Laid-Open No. H06-242378, and Japanese Patent Application Laid-Open No. 2001-21804).
Here, in the three-unit inner focus type, the first lens unit having positive refractive power includes, in an order of from the object side to the image side, a front first lens unit having negative refractive power, a middle first lens unit having positive refractive power, and a rear first lens unit having positive refractive power. In the focusing method thereof, the middle first lens unit is moved to the image plane side when focusing from an object at infinity to an object at short distance.
Japanese Patent Application Laid-Open No. H06-242378 discloses a large diameter and high zoom-ratio zoom lens having a zoom ratio of approximately 8.0 to 17.6, a photographing angle of field (angle of field) of approximately 65 to 87 degrees at a wide angle end, and an F number of approximately 1.6 to 2.2.
Japanese Patent Application Laid-Open No. 2001-21804 discloses a large diameter and high zoom-ratio zoom lens having a zoom ratio of approximately 8.0 to 14.9, a photographing angle of field (angle of field) of approximately 79 to 88 degrees at a wide angle end, and an F number of approximately 1.6 to 2.1.
For the positive lead type four-unit zoom lens having the above-mentioned structure, it is relatively easy to realize a high zoom ratio.
However, as the zoom ratio becomes higher, variations of various aberrations become larger, and hence it becomes difficult to obtain high optical performance over the entire zoom range.
In particular, both in axial chromatic aberration and in lateral chromatic aberration, a zoom (zoom variation) increases. Therefore, in order to obtain high imaging performance, it is important to appropriately correct not only primary chromatic aberration but also secondary spectrum.
In the positive lead type four-unit zoom lens using the three-unit inner focus type, in order to achieve a higher zoom ratio and to appropriately correct chromatic aberration so that high optical performance can be obtained, it is important to appropriately set a structure of the front first lens unit located closer to the object side than the magnification-varying lens unit.